In these, abstract images on the filmstrip shape the projector beam into a three-dimensional light form, made visible by the introduction of smoke into the space. McCall has said that the films act as "stencils" for projected light; the images are transparent, while the black background on which they are drawn is opaque. As light passes through the images, it takes their shape in three dimensions. Arcs, cones, and blades of light grow, pulsate, or sweep dramatically through space. In Line Describing a Cone, for example, a white point within the black film frame traces an arc, then a complete circle. The resulting 3-D light form evolves from a line into a hollow cone of light, forming a point at the projector lens. The cone form is put through a series of permutations in Conical Solid, Partial Cone, and Cone of Variable Volume (all 1974). In Long Film for Four Projectors (1974) and Four Projected Movements (1975), straight lines drawn diagonally across the frame produce flat blades of light that scan the exhibition space. The films require total darkness; any stray ambient light must be extinguished, and the projector, placed within the exhibition space, must be covered to prevent light spillage.

The solid light films enacted a process of cinematic abstraction in which the removal of representational imagery was only the beginning. The films dispense with the screen and two-dimensionality itself, a quality long singled out by essentialist theorists as a necessary condition of film. Since the films encourage viewers to interact with the light beam and look at it from multiple perspectives, the ideal space for the solid light films is an open, empty one more like the gallery than the auditorium. McCall also dropped the convention of the seated, immobile cinema audience, taking up the norms of gallery spectatorship instead. In Long Film for Four Projectors, for instance, the repeated reloading of reels onto the projectors extends the duration of the film to six hours, with viewers coming and going at will rather than assembling at a specific time to watch the film from start to finish. In spatial terms, the film creates a field of projected light without the single focal point (the screen) of other films. Hence, its space and time engender the type of spectatorial experience more commonly thought of as sculptural.

McCall's peeling away of cinematic materials and exhibition conventions culminated in Long Film for Ambient Light (1975), a 24-hour event, entirely film-less, consisting of an empty loft space illuminated by diffused window light during the day and a bare light bulb at night. A schedule isolating one 24-hour cycle of the work within a 50-day span and an artist's statement were attached to one wall. In the statement, "Notes in Duration," McCall linked Long Film for Ambient Light to his fire events; both possessed an expanded spatial and temporal scale that mitigated against the formation of an audience, enabling a "one-to-one relationship between spectator and work." But despite the work's affinities with performance and sculpture, its location in a gallery-type space, and the fact that it involved no film, McCall asserted it as a film, placing it firmly within avant-garde cinema's long tradition of film-ontological investigation: "I am now interested in reducing the 'performance' aspect, in order to examine other fundamentals, viz temporality, light. I am presently assuming that it is possible to do this without using the customary photochemical and electro-mechanical processes…"

McCall's remark suggests that a work without film could still be a "film" if it possessed certain fundamental cinematic properties, identified here as light and time. An influential text in this regard was Metaphors on Vision, Brakhage's summation of his aesthetics written in 1960. Reading the text for the first time in late 1972 or early 1973, McCall must have taken special interest in Brakhage's ecstatic proclamations about projected light:

Believe in [film] eye-wise, and the very comet of its overhead throw from projector to screen will intrigue you so deeply that its fingering play will move integrally with what's reflected, a comet-tail integrity which would lead back finally to the film's creator. I am meaning, simply, that the rhythms of change in the beam of illumination which now goes entirely over the heads of the audience would, in the work of art, contain in itself some quality of a spiritual experience.

Brakhage anticipates expanded cinema, the radical broadening of film beyond the bounds of the "customary photochemical and electro-mechanical processes." Film is liberated not only from the limitations of mimesis, but from the material constraints of the medium itself. This opening up of the category of cinema was also an "opening out" of film into three-dimensionality. From this expansive logic came the concept of "cinematic space," the object of intensive investigation by the next generation of avant-garde filmmakers, especially those associated with the London Filmmakers' Coop.

McCall began attending LFMC screenings in 1970, and showed his own work there after moving to the U.S. He has spoken of the influence of the Coop, particularly its emphasis on spectatorial activity within the space of the cinema. This activity was usually considered in cognitive terms, most famously in 'structural-materialist' films that placed special demands on viewer cognition, the primary goal of politically-engaged avant-garde cinema stretching back at least to the Soviets. But McCall and others (including Lis Rhodes, William Raban, and Malcolm Le Grice) extended the notion of the active viewer to the physical sphere with films that drew attention to their surroundings and encouraged participation and interaction. In this context, "space" was not a sculptural value relevant only to gallery viewing, but a feature of cinema. As object-based art like painting and sculpture took on a temporal dimension (in "action" interpretations of Abstract Expressionism and phenomenological readings of minimalism), film gained a spatial dimension. The reigning conception of "duration" among avant-garde filmmakers at the time merged both vectors - temporal and spatial - into a single phenomenal experience. McCall's projected light forms, unfolding simultaneously in time and space, are particularly vivid embodiments of this concept, and of avant-garde film's exploration of new forms, spaces, and modes of spectatorship.